This invention relates generally to mechanical positioning devices of the type which translate or transport a nut or the like component to and fro along a shaft or lead screw of finite length which has longitudinally extending transport elements such as grooves or helical threads therein and more particularly to a balanced component or nut to be mounted on and disposed in operative association with a shaft or lead screw of finite length having either longitudinal grooves, or single or multi-start helical threads wherein rotational play or linear backlash is prevented from developing between the coating elements regardless of the direction of movement of the balanced component or nut and which provides means to adjust the predetermined torque required to move the balanced component along the associated shaft and is self adjusting to take up wear so as to prolong the operating life of the balanced component or nut.
The term "balanced" when used herein in association with the improved component or nut in accordance with the present invention will mean that the torque required to produce relative movement between the shaft or lead screw and the component or nut will be the same regardless of the direction of movement.
The use of elongated shafts or lead screws of finite length with longitudinally extending grooves or longitudinally extending helical threads for transporting therealong or for relative movement therewith, of nuts or movable components with mating lands or threads is employed in many widely used products such as dictating machines, variable capacitors, variable resistors, potentiometers, and similar devices which require the movement of one element across another. For example in dictating machines a helically threaded shaft or lead screw will transport the recording stylus across a recording device such as a record or a belt. In the variable resistor, a contact arm is moved back and forth across a resistance coil.
The main problem in positioning devices of this type is the fact that it is difficult to obtain accurate positioning during this relative movement due to problems of rotational play and/or backlash between the given shaft or lead screw and the component or nut associated therewith. This is particularly so in positioning devices where the mating helical threads are made to standard interchangeable fits such as is called out in Mil-Spec 7742 or in U.S. Government Handbook No. 28.
Various efforts have been made in the prior art devices to overcome this problem such as is shown in U.S. Pat. No. 3,831,460, 3,656,358, 3,364,757 and 2,793,538.
In the present invention this problem is overcome by means of an improved balanced component which provides a compression means at a medial point transverse to the longitudinal axis of the balanced component so that it makes no difference which direction the component is moved during translation or transportation of the balanced component relative to a given shaft.
Additionally, however in the improved construction in accordance with the present invention the compression means can adjust the compression forces exerted at the medial section of the component so that a predetermined torque will be required to move the component to and fro along the associated shaft on which the component is mounted. Further, the compression forces will also act so as to take up any wear which may occur between the associated elements so that the accuracy of a positioning device which includes these elements will be prolonged.